1. Field of the Invention
The present invention generally relates to digital imaging apparatuses, and particularly relates to a method of setting parameters for use in the color processing of images taken by a digital imaging apparatus.
2. Description of the Related Art
In digital cameras, a color filter comprised of a Bayer array in which the three primary colors R (red), G (green), and B (blue) are arranged is placed in front of the solid-state imaging device such as a CCD sensor or CMOS sensor, so that light passing through the color filter is broken down into color components. In such a Bayer array, every four pixels having two pixels in height and two pixels in width are taken as a set in the pixel matrix of the imaging device, and is configured to include two green pixels, one red pixel, and one blue pixel. Since the sensitivity of human vision is high with respect to the luminance of green component, the proportion of green pixels in the Bayer array is set high in order to enhance luminance resolution.
Data obtained immediately after passing through the Bayer array is referred to as raw data. Color processing (also referred to as “development”) is performed on the raw data to generate RGB image data.
If the number of pixels of the imaging device is M×N pixels, the pixel value of a pixel of interest needs to be derived through interpolation using the pixel values of surrounding pixels around the pixel of interest in order to generate a RGB color image of M×N pixels. Color interpolation processing based on an interpolation algorithm is performed on each pixel so as to generate RGB image data from raw data.
In color processing, rounding error (quantization error) occurs during the computation, resulting in a shift in hue. Such hue shift may be suppressed by performing the color processing under optimum image conditions based on the adjustment of white balance and luminance.
An interpolation algorithm and various parameters (e.g., parameters used in the algorithm, white balance, luminance, and so on) for color processing are stored as color processing firmware in a ROM inside a digital camera. The image processing LSI executes this firmware at the time of imaging so as to generate color image. The algorithm and various parameters for color processing greatly affect the quality of color images taken by a digital camera. Digital camera manufacturers thus compete against each other in terms of the superiority of image quality by using uniquely developed algorithms.
When digital camera products are developed, the above-mentioned various parameters are adjusted at the final-stage of development in order to achieve beautiful color image quality. In this adjustment, raw data obtained by using a real digital camera is transferred to a computer such as a personal computer via a communication path such as a USB. The computer performs software-based color processing to generate a color image, which is then visually inspected to adjust the various parameters. The color processing software used in this process is designed to simulate the color processing to be embedded in the digital camera product that is being developed.
When the various parameters are determined, the determined parameters are written to the ROM inside the digital camera. The digital camera is then actually used to take and develop images so that the final check of image quality is performed.
The method of parameter adjustment described above has a problem in that the color processing algorithm that is preferably kept as secret from outside the company is turned into software, so that the details of the color processing algorithm can be analyzed from the color processing software. Further, the speed of image processing by use of color processing software is extremely lower than the speed of image processing by use of an image processing LSI. Processing that is completed in one second for one image by use of an image processing LSI may take longer than one minute if it is performed by use of color processing software. Further, there is a problem in that the labor to turn a complex color processing algorithm into software is necessary.
In order to obviate the problems described above, the ROM of the digital camera that stores color processing firmware may be rewritten to set various parameters, and, then, imaging and image quality evaluation are performed, followed by readjusting the various parameters based on the image quality evaluation. Such method, however, requires a significant amount of time and labor since a sequence of imaging, image quality evaluation, modification to the firmware, and rewriting of the ROM needs to be performed several times.
Accordingly, there is a need for a digital camera and method of setting color processing parameters that allow parameters regarding color processing to be adjusted with a small amount of time and labor.
[Patent Document 1] Japanese Patent Application Publication No. 2004-120541